The present invention is directed to a dowel assembly which can be anchored in a borehole in a receiving material, such as concrete, masonry or the like. An abutment on the dowel assembly is stressed relative to the receiving material so that a part can be placed between the abutment and the receiving material so that it is secured on the surface of the material.
Dowel assemblies intended for higher load as well as cyclic loads are loaded in the axial direction after being anchored in the receiving material. The axial loading is largely independent of whether the dowel assembly is anchored in the receiving material in an expansion operation, by a positive locking engagement, or by an adhesive connection, such as by using a cement product. The axial loading is of great significance if high dynamic forces act on the dowel assembly through a connection, if the static friction between the receiving material and the connection is required for absorbing lateral stresses or for supporting brackets with long cantilevered sections. Research has revealed that the axial load generated by the anchoring of the dowel assembly in the receiving material is considerably reduced after a short period of time. This reduction in the axial loading, which can be ascribed to a "flowing" or relaxing of the receiving material, can amount to 30 to 80% of the original axial force. The reduction develops immediately after the establishment of the axial force, it reaches approximately 25% after about two hours and amounts to about 35% after approximately seven days. An increase in the original axial force (for instance by approximately 50% above the anticipated force) can, however, not prevent the reduction in the axial force below the required force after a short time and, accordingly, the desired axial force cannot be maintained. By loading the dowel assembly to a multiple of the desired load, the time in which the reduction of the applied axial load below the required load is merely delayed. By overloading the dowel when it is originally stressed, the strength of the receiving material may be exceeded which could result in immediate or subsequent damage.
Up to the present time, one means for avoiding this disadvantageous phenomenon has been to retighten the dowel assembly by a certain amount after the original axial load has dropped off. The retightening step, however, requires time and money and is relatively difficult to control. Furthermore, the accessibility of the attachment after the installation of the dowel assembly is completed is often very limited. Moreover, such an adjustment feature has only a delaying action.
Another solution to this known problem has been to place spring elements between the abutment on the dowel assembly and the receiving material or the component can be attached to the receiving material with the maximum load provided exceeding the allowable load on the dowel. Such spring members are complicated and of considerable size. Further, they can be partly or completely impaired by corrosion. The sizing and location of the spring elements also provides problems. Since a number of spring elements are required for the desired spring characteristic, there is the possibility that a portion of the spring elements may be lost or incorrectly installed during the placement of the dowel assembly so that the desired spring characteristic is not achieved.